Desludging System for Electrolytic Cells

ABSTRACT

The invention relates generally to a desludging system for electrolytic cells for metal production in the hydrometallurgical industry. Specifically, it relates to a system for desludging cells, preferably for copper cathodes, which comprises removable collectors for lead sludge accumulated at the bottom of cells. Collectors are located at the bottom of the cell and lead sludge is transported towards trays which are later removed from the cell with the sludge thereon without having to stop the cathode production.

FIELD OF INVENTION

The invention relates generally to a desludging system for electrolyticcells for metal production in the hydrometallurgical industry.Specifically, it relates to a system for desludging cells, preferablyfor copper cathodes, which comprises removable collectors for leadsludge accumulated at the bottom of cells. Collectors are located at thebottom of the cell and lead sludge is transported towards trays whichare later removed from the cell with the sludge thereon without havingto stop the cathode production.

BACKGROUND

In cathode production processes in the metallurgic industry, includingcopper cathode production processes, lead anodes oxidize to form leadoxide which separates and precipitates to the bottom of the cell where asludge is built-up. This sludge must be extracted regularly to preventlead contamination of the copper cathodes.

Regular desludging from electrowinning cells requires stopping thedirect current which is necessary for metal electrowinning. To avoidcontamination, circuit breaker frames are used to isolate the cell to becleaned while the sludge is being removed. The above implies that thecopper cathode production in such cells has to stop.

One solution applied to cell desludging is disclosed in the Chileanpatent application for invention number 987-2002 which describes aprocess and the equipment for cell desludging in electrolytic processplants where solid particles separate in the electrolyte solution insidethe electrolytic cell. The equipment comprises a vacuum that suckssolids without spreading them in the electrolyte solution. Then, thesolids are separated by their size and weight, and then the collectedsludge is packaged. However, the system costs per cell for desludgingare costly, since this desludging process also involves filtersaturation and vacuum pump wear out. Additionally, vacuum operation forcollecting the mud sediments from the bottom of each cell is very slow.

SUMMARY OF THE INVENTION

The main problem solved by this invention comprises desludging a cellwithout having to stop current supply during the process. Thus, metalelectrowinning on cathodes can continue uninterruptedly and time duringfinal harvest is not wasted.

In one aspect, the present invention provides a desludging system forelectrolytic cells for metal production in the hydrometallurgicalindustry. In a preferred embodiment, the desludging system operateswithout having to stop the current supply of cells thereby stoppingcathode production. For example, the desludging system may comprise acollector formed by a continuous belt device with a feed rolleractivated by a driving system and a free roller joint by a pair ofparallel rails which join the axles in each roller. In one embodiment, acontinuous belt is placed and the sludge from the electrowinning processis deposited thereon. At the ends of the continuous belt device andadjacent to the narrow ends of the electrowinning cell, one or moreremoval trays may be installed to receive sludge accumulated on thecollector continuous belt and such feed is produced by activating thedriving system on the feed roller and consequently the free roller.

These and other aspects of the invention will be better understood byreference to the following detailed description and drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1: shows an isometric view of the invention, which illustrates twosystems installed at the bottom of a cell.

FIG. 2: shows an isometric view of the invention wherein the frameworkand rails where collector belts move can be seen.

FIG. 3: shows an isometric view of the invention, as in FIG. 1, butincluding open removal trays.

FIG. 4: shows an isometric view of the invention, as in FIG. 3 but withthe removal trays at the bottom of the cell, now open and ready to bedesludged.

FIG. 5: is a top plan view with a drawing of side elevation view of thebelt rotary device.

FIG. 6: is a top plan view of the belt rotary device with its drivingrollers that make belts rotate.

FIG. 7: is an isometric perspective view representing a cell in whichthe size of the cell only allows one system of the invention to beinstalled.

DETAILED DESCRIPTION OF THE INVENTION

Generally, the invention comprises a system of sludge collectorsinstalled at the bottom of a cell. The collector is a flat, continuousbelt which captures lead oxides which separate from the anodes beforereaching the bottom of the cells. The lead sludge captured by collectorsis accumulated over time. When it is time for desludging, the belts areactivated to convey the sludge under the cathodes and anodes towards oneor more removal trays which receive the sludge. Then, the removal traysare removed from the cell for its final destination. Once the sludge hasbeen removed from the trays, these are placed back into cells waitingfor the next desludging. There may be as many systems installed as cellsinside the electrowinning plant, and the number of systems per cell willdepend on the size of them.

In one embodiment according to the invention, it is possible to makeonly one investment per cell, with just the normal cost of desludgingand with minimum of personnel, thus cutting desludge time and cost byhalf compared to the vacuum technique. That is to say, for the samecost, with this invention, it takes the same time to remove residuesfrom 2 cells compared to the amount of time spent in vacuuming just onecell.

One process for desludging cells involves extracting lead sludgeproduced in copper electrowinning cells by stopping production via acircuit breaker frame which stops the electrical supply in 2 or 3 cellsto be desludged. During this process, the production is stopped at least1.5 hour per cell when a run-through operation circuit breaker frame isused, and three hours per cell when only the standard frame is used,with a desludging frequency from two to three months per each cell inthe electrowinning plant.

Individual mining tasks may have their own desludging procedure, basedon the available resources. A general desludging procedure may be asfollows:

1. A Gantry Crane is assembled to the Circuit Braker Frame in the cellsto be desludged. Current supply is shut-off and the copperelectrowinning on stainless Cathodes is stopped.2. All Stainless-steel Cathodes with electro deposited copper areremoved by the Gantry Crane.3. All Lead Anodes are removed by the Gantry Crane.4. All anti-fog spheres, which are floating on the electrolyte, areremoved manually.5. Then, when the stopper at the bottom of the cell is removed allelectrolyte is emptied by gravity.6. When the Cell is completely empty, Lead Sludge settled at the bottomcan be observed. This sludge is swept, extracted and placed into specialcontainers.7. The bottom of the Cell is washed with clean water.8. The stoppers are installed again and the process for filling withelectrolyte is started.9. Anti-fogs Spheres are added.10. Anodes are placed by the Gantry Crane.11. Cathodes are placed by the Gantry Crane12. The Circuit breaker frame is removed by the Gantry Crane and thecurrent supply is switched-on inside the desludged cells.13. The Circuit Breaker Frame along with the Gantry Crane is taken toother cells to be desludged followed by step 1 and so on until everyCell inside the Plant has been desludged.

The present invention separates the desludging process in leadcontaminated cells from the copper cathode harvest. Therefore, a gantrycrane is not necessarily a required element for the system according tothe invention compared to traditional desludging. In this way, thepresent invention provides for more gantry crane availability forcarrying out gantry crane basic tasks such as copper cathode harvesting.This allows for increased copper cathode production per cell, morefrequent desludgings, and improved copper cathode quality by reducinglead contamination present in the accumulated sludge.

In one embodiment, the system of the invention comprises a collector (2)which consists of a continuous belt device with a feed roller (3)activated by a driving system (10) which make the belt move towardsnarrow ends of the electrowinning cell (1). Additionally, the continuousbelt device comprises a free roller (4) which guides the belt when theroller (3) is activated. The continuous belt device comprises parallelrails (8) which join axles (9) which are part of the roller (3) drivenby the driving system (10) and also the free roller (4). Both rollersare joined by a belt (11) which makes the rollers move at the samespeed, consequently the belt moves at the same speed with the sludgeaccumulated thereon, as shown in FIG. 6.

At the ends of the continuous belt device and adjacent to the narrowends of the electrowinning cell are located the removal trays (7) whichreceive the sludge (12) that accumulates on the collector belt (2).

In one embodiment according to the invention, the continuous belt devicealso comprises a framework (5) formed by lateral bars (6) supportingparallel rails (8) which support both the drive roller (3) and freeroller (4), forming a firm structure where the collector continuous beltmoves on (2). The framework has a rectangular shape so that it includesthe complete area where oxides are separated, leaving a space at theends of the framework to install the removal trays (7) when desludgingoccurs. The framework is fitted onto later bars (6) through dovetailswhich enable such framework (5) to keep its position within the system.This framework works as a guide and a support for continuous belts whichreceive and transport the sludge thereon.

According to one embodiment of the invention, the removal trays (7) mayremain out of the cell during the period the collector is in its steadystate accumulating the sludge thereon. Additionally, a removal tray mayhave a rectangular shape where its width is slightly narrower than thewidth of the cell, and its height is such that it enables to incorporatea multiple section labyrinth type cap which helps to encapsulate thesludge transferred by the belt. A tray's base may have a rubber borderthroughout the rectangular perimeter which is in contact with the cup inorder to seal the tray before it is taken from the cell.

A high relief border may be incorporated at lateral ends of continuousbelts to prevent the sludge from moving sideward, thereby spreading thesludge towards the bottom of the cell. Likewise, this system maycomprise at the driving roller zone (3) a sludge scraper to clean theremaining sludge on the continuous belt.

In one embodiment, the system according to the invention may bemanufactured with materials which are preferably acid resistantmaterials and which do not conduct electricity like synthetic rubber,polyethylene plastics, polypropylene or the like.

Depending on the size of the cell, all the systems necessary may beinstalled, as shown in FIG. 1 which illustrates a cell with two systemsinstalled.

1. A desludging system for electrolytic cells for metal production in the hydrometallurgical industry, which operates without having to stop current supply of cells thereby stopping cathode production, comprising in said system a collector formed by a continuous belt device with a feed roller activated by a driving system and a free roller joint by a pair of parallel rails which join the axles in each roller, whereon a continuous belt is placed and the sludge from the electrowinning process is deposited thereon; at the ends of the continuous belt device and adjacent to the narrow ends of the electrowinning cell, one or more removal trays have been installed which receive the sludge accumulated on the collector continuous belt and such feed is produced by activating the driving system on the feed roller and consequently the free roller.
 2. A desludging system according to claim 1, wherein such continuous belt device also comprises a framework formed by lateral bars which support such parallel rails which support both the driving roller and free roller forming a firm structure where the collector continuous belt moves.
 3. A desludging system according to claim 2, wherein the framework has a rectangular shape and comprises the complete area where oxides separate within the cell, leaving a space at the ends in order to install removal trays for desludging.
 4. A desludging system according to claim 3, wherein the framework is fitted onto parallel bars through dovetails which enable such framework to keep its position within the system.
 5. A desludging system according to claim 1, wherein said removal trays have a rectangular shape with a width slightly narrower than the width of the cell, and a height such that the height enables the incorporation of a multiple section labyrinth type cap which helps to encapsulate the sludge transferred through the continuous belt.
 6. A desludging system according to claim 5, wherein the base of the tray has a rubber border throughout the rectangular perimeter which is in contact with the cup in order to seal the tray before it is taken from the cell with the sludge therein.
 7. A desludging system according to claim 1, wherein a high relief border is incorporated at lateral ends of the continuous belt to prevent sludge from moving sideward, thereby spreading the sludge towards the bottom of the cell.
 8. A desludging system according to claim 1, wherein the system further comprises at a driving roller zone a sludge scraper to clean any remaining sludge on the continuous belt.
 9. A desludging system according to claim 1, wherein the system is manufactured with materials which are acid resistant materials and which do not conduct electricity.
 10. A desludging system according to claim 9, wherein said materials are synthetic rubber, polyethylene plastics, polypropylene or the like.
 11. A desludging system according to claim 1, wherein a cell may include as many systems as possible depending on its size in order to include the complete area where the material to be desludged may fall. 